The present invention concerns a weft feeder for weaving looms.
It is known that weaving looms using as weft insertion means a carrier other than the shuttle, namely gripper looms, projectile looms and, lastly, air and water looms, require--for a proper working--the weft to be fed therein at a low and most regular tension.
It is also known that, in order to obtain this result, devices called weft feeders, or weft presenting devices, have already been adopted since some time in said looms, said devices being positioned between the bobbin--from which the weft is picked--and the loom insertion means, and forming a weft reserve wound on a drum in the form of successive turns, the unwinding of which takes place at a practically constant tension, the value of which is furthermore adjustable, thanks to a braking system at the outlet of the drum.
The object of the present invention is to provide important improvements in weft feeders of the type--since long developed and now generally preferred by loom constructors--wherein the drum around which the weft yarn winds to form the reserve is held stationary, while the turns of said reserve are laid thereon by a rotating reel and are moved forward, mutually spaced, by a set of columns prevented from rotating in respect of said drum, but partially and variably emerging from seats provided in its periphery.
As is known, it is very important in weft presenting devices not only to obtain a perfect arrangement of the yarn reserve turns, but also to be able to easily control the amount of yarn reserve present on the winding unit. While in weft presenting devices wherein the yarn reserve moves forward by adjacent turns, said control is advantageously performed by means of a photoelectric cell fixedly connected to the body of the apparatus, in the devices of the type heretofore described, wherein the turns are moved forward mutually spaced, it is necessary to make use of mechanical weft feelers. The photoelectric cell usually comprises a sending element and a receiving element, arranged so that the beam of light sent by the first element may be intercepted by the second through reflection from the actual yarn, or else onto a reflecting element applied on the winding drum. In the first case, the yarn presence modifies the electric signal outgoing from the photoelectric cell unit, due to the presence of a reflection on the yarn, while in the second case, the electric signal is modified through the presence of yarn preventing the reflection of the beam of light. In weft presenting devices where the yarn moves forward by adjacent turns, this is allowed--in the first case--by the fact that the adjacent turns form a reflecting surface with appropriate characteristics, and--in the second case--by the fact that the adjacent turns are adopted to provide a compact screen for the reflecting element.
In weft presenting devices where the yarn moves forward by mutually spaced turns--which are preferred because the advancement of the turns on the winding unit, controlled by the mobile columns, determines a uniform tension between the various turns laid, which makes the evenness of the reserve less strictly connected to the continuous rotation of the motor, than in weft presenting devices where the yarn moves forward by adjacent turns--it has up to date not been possible to read and control the amount of the reserve with the previously described photoelectric cell methods, due to the considerable spacing between the turns, which gives rise to uncertainties and even serious errors.
At present, in such devices, the yarn reserve is hence controlled by means of finger micro-switches, fixed to the outer body of the presenting device and whose fingers, bearing on the wound turns, indicate the presence thereof. The lack of turns on the winding unit, as they are fed to the loom, causes a lowering of the finger with a corresponding electric signal which, by rotating again the electric motor, allows the re-winding of new turns. However, the presence of the micro-switch finger, due to its physical contact with the wound turns, is prejudicial to the regular positioning thereof. In fact, especially if the yarn is very fine, the turns tend to fall out of order, determining tension variations at the outlet of the weft presenting device.
Even if attempting to overcome this drawback by adjusting the pressure of the finger on the turns (by acting on the spring which pre-loads the fingers, so as to apply only a slight pressure in case of very fine yarns), the inconvenience still remains in case of very thick yarns. In this event, in fact, the winding turn may stop in correspondence of the micro-switch finger, thereby indicating the presence of yarn reserve while this may be missing. It can therefore be easily understood how important it is to extend the use of photoelectric cell yarn detectors to weft feeders wherein the yarn moves forward by mutually spaced turns. This use would furthermore allow a more efficient control of the motor speed, which leads to the winding of new turns and to the picking of weft by the loom.
The technical improvements according to the present invention therefore concern a weft feeder, wherein an attempt has been made to combine the positive characteristics of the previous systems for moving forward the yarn reserve turns on the winding drum, so as to improve its performance, reducing at the same time the controls to a minimum in order to facilitate the use thereof.
Concerning the system adopted to move forward the turns of yarn reserve, the traditional system of mutually spaced turns has thus been adopted, modifying however the arrangement of said turns along the longitudinal axis of the winding unit. The turns are in fact moved forward by means of columns moving partially and variably emerging from the drum, while the configuration of the arrangement has been modified so as to obtain a progressive accumulation of said turns towards the outlet zone of the winding unit. This arrangement has allowed using a first reserve zone, with turns separated physically one from the other and having a uniform tension, and a second reserve zone, where the turns are first close and then in contact, so as to move forward by pushing, though being prevented from overlapping by the fact that the tension in said turns is now uniform.
This second zone of the reserve, where the turns lie in contact, allows reading and control with the help of photoelectric cell devices. In this zone, in fact, the adjacent turns form a surface whereon it is possible to obtain directly the reflection of the beam of light sent by the photoelectric cell, or preferably--to avoid the influence of the yarn colour, thereby providing a more efficient and reliable solution--said turns are adapted to form a compact screen for the reflecting element.